1. Field of the Invention
The present invention relates to systems and methods for delivering drugs to a patient. In particular, the present invention relates to systems and methods for more efficient and controlled subcutaneous infusion of drugs or substances.
2. Background
Diabetes is a very serious illness affecting millions of people today. Many diabetic patients require injection of insulin to maintain proper levels of glucose in their blood in order to survive. Such injections of insulin are done using various drug delivery systems.
Many medical treatment systems and methods involve drug delivery systems that employ subcutaneous infusions of therapeutic fluids, drugs, proteins, and other compounds. Such delivery systems and methods, especially in the area of insulin delivery, have made use of subcutaneous catheters and continuous subcutaneous insulin infusion (“CSII”) pumps. In conventional insulin pumps, the pump can be attached to a disposable thin plastic tube or a catheter through which insulin passes into the tissue. The catheter can be inserted transcutaneously, typically through the skin of the patient's abdomen, and is changed every two to three days. New types of insulin pumps, such as the OmniPod pump manufactured by Insulet Corporation, do not have an external catheter and, instead, a catheter port is embedded into the pump mechanism.
In many instances, patients require insulin delivery around the clock to keep proper levels of glucose in their blood. Insulin can be delivered at a basal rate or in bolus doses. The basal rate represents insulin that is continuously delivered to the patient. Such a continuous delivery of insulin keeps the blood glucose level in the desired range between meals and overnight. The bolus dose is an amount of insulin delivered to the patient according to food intake at meals, particularly carbohydrates. When patient consumes food, his or her levels of glucose rise. Some conventional pump mechanisms are configured to react upon command, or by way of an automated procedure, to the increase in glucose levels by delivering a bolus dose of insulin that matches the rise in the level of glucose and prevents large fluctuations in glucose levels. However, this attempt at control is confounded by the fact that there is usually a variable profile of the absorption of insulin from the injection site to the blood circulation. This variability of the insulin absorption results in an error of up to 30% in insulin levels in the blood and hence results in variability of the insulin effect. Such variability in turn causes extreme variability in the resulting glucose levels, which may cause hyperglycemic and hypoglycemic events; in any case such variability itself has been shown to be potentially damaging to organs and body systems. (See, e.g., Lutz Heinemann, “Variability of Insulin Absorption and Insulin Action”, Diabetes Technology & Therapeutics, Vol. 4 No 5, 2002).